The gigantic Central Post Office in Helsinki/Helsingfors was built in 1938 in accordance with functionalist principles. In other words, it may not have been pretty, but it worked. Today, the building contains a branch post office and a few shops, but is being redeveloped to offer various additional attractions.
Here it is in 1942, engraved by Arthur Schuricht. It's so huge and impressive that the top of the frame can't contain it!

And here's a site describing how it's being adapted today.
https://postitalo.fi/en/